[core] look for loaded parent tiles in cache (#4595)

fix #4047

port https://github.com/mapbox/mapbox-gl-js/pull/2158

2 files changed, 9 insertions, 3 deletions

diff --git a/src/mbgl/source/source.cpp b/src/mbgl/source/source.cpp
index 14fd62348b..47efbe9088 100644
--- a/src/mbgl/source/source.cpp
+++ b/src/mbgl/source/source.cpp
@@ -328,7 +328,7 @@ bool Source::findLoadedChildren(const TileID& tileID, int32_t maxCoveringZoom, s
  *
  * @return boolean Whether a parent was found.
  */
-void Source::findLoadedParent(const TileID& tileID, int32_t minCoveringZoom, std::vector<TileID>& retain) {
+void Source::findLoadedParent(const TileID& tileID, int32_t minCoveringZoom, std::vector<TileID>& retain, const StyleUpdateParameters& parameters) {
     for (int32_t z = tileID.z - 1; z >= minCoveringZoom; --z) {
         const TileID parent_id = tileID.parent(z, info->maxZoom);
         const TileData::State state = hasTile(parent_id);
@@ -338,6 +338,12 @@ void Source::findLoadedParent(const TileID& tileID, int32_t minCoveringZoom, std
                 return;
             }
         }
+
+        if (cache.has(parent_id.normalized().to_uint64())) {
+            addTile(parent_id, parameters);
+            retain.emplace_back(parent_id);
+            return;
+        }
     }
 }
 
@@ -400,7 +406,7 @@ bool Source::update(const StyleUpdateParameters& parameters) {
             // Then, if there are no complete child tiles, try to find existing
             // parent tiles that completely cover the missing tile.
             if (!complete) {
-                findLoadedParent(tileID, minCoveringZoom, retain);
+                findLoadedParent(tileID, minCoveringZoom, retain, parameters);
             }
         }
     }
diff --git a/src/mbgl/source/source.hpp b/src/mbgl/source/source.hpp
index c85e2ccd2d..1aad191a5c 100644
--- a/src/mbgl/source/source.hpp
+++ b/src/mbgl/source/source.hpp
@@ -88,7 +88,7 @@ private:
                              bool isNewTile);
     bool handlePartialTile(const TileID&);
     bool findLoadedChildren(const TileID&, int32_t maxCoveringZoom, std::vector<TileID>& retain);
-    void findLoadedParent(const TileID&, int32_t minCoveringZoom, std::vector<TileID>& retain);
+    void findLoadedParent(const TileID&, int32_t minCoveringZoom, std::vector<TileID>& retain, const StyleUpdateParameters&);
 
     TileData::State addTile(const TileID&, const StyleUpdateParameters&);
     TileData::State hasTile(const TileID&);